For example, certain Internet service providers do not allow their customers to send bulk unsolicited emails, or "spam." Customers who send spam would be in violation of the provider’s terms of service, but would not qualify as trespassers – both because they are authorized users and because they have an existing contractual relationship with the provider. If, however, an intruder gained unauthorized access to the ISP network and sent spam to millions of victims, the intruder would be a trespasser because he did not have authority to access any part of the network. Because the identity of the intruder is generally unknown at the time monitoring begins, the ISP does not “know” that there is an existing contractual relationship and the trespasser is not excluded from the definition of a trespasser.